The disclosure relates to articles with retained strength, and more particularly to articles including a substrate and a patterned coating disposed on a surface of the substrate and methods of forming such articles.
Articles including substrates such as glass substrates, which may be strengthened or strong as described herein, have found wide usage recently as a protective cover glass for displays, especially in touch-screen applications, and there is a potential for its use in many other applications, such as automotive or architectural windows and glass for photovoltaic systems. In many of these applications it can be advantageous to apply a coating to the substrates. Exemplary coatings include indium-tin-oxide (“ITO”) or other transparent conductive oxides (e.g., aluminum and gallium doped zinc oxides and fluorine doped tin oxide), hard coatings of various kinds (e.g., diamond-like carbon, Al2O3, AlN, AlOxNy, Si3N4, SiOxNy, SiAlxOyNz TiN, TiC), IR or UV reflecting layers, conducting or semiconducting layers, electronics layers, thin-film-transistor layers, or anti-reflection (“AR”) coatings (e.g., SiO2, Nb2O5 and TiO2 layered structures). In many instances these coatings must necessarily be hard and brittle, or otherwise their other functional properties (e.g., mechanical, durability, electrical conductivity, optical properties) will be degraded. In most cases these coatings are thin films, that is, they generally have a thickness in the range of 0.005 μm to 10 μm (e.g., 5 nm to 10,000 nm).
When a coating is applied to a surface of such substrates, the average flexural strength of the substrate may be reduced, for example, when evaluated using ball-drop or ring-on-ring strength testing. This behavior has been measured to be independent of temperature effects (i.e., the behavior is not caused by significant or measureable relaxation of surface compressive stress in the strengthened glass substrate due to any heating). The reduction in average flexural strength is also apparently independent of any substrate surface damage or corrosion from processing, and is apparently an inherent mechanical attribute of the article, even when thin films having a thickness in the range from about 20 nm to about 200 nm are utilized in the article. In view of this new understanding, there is a need to prevent coatings from reducing the average flexural strength of substrates and articles including the same.
The embodiments of the articles described herein exhibit strength retention by preventing or suppressing crack formation in the coating by, for example, enhancing the intrinsic strain-to-failure of the coating and/or providing a mechanism of strain relief in the coating.